AppViewModel.cs

using Frogy.Views;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Input;

namespace Frogy
{
    class AppViewModel
    {
        public ICommand ShowWindowCommand
        {
            get
            {
                return new DelegateCommand
                {
                    CanExecuteFunc = () => true,
                    CommandAction = () =>
                    {
                        if (Application.Current.MainWindow == null)
                            Application.Current.MainWindow = new DashboardView();

                        Application.Current.MainWindow.Show();
                        Application.Current.MainWindow.Activate();
                    }
                };
            }
        }

        public ICommand HideWindowCommand
        {
            get
            {
                return new DelegateCommand
                {
                    CommandAction = () => Application.Current.MainWindow.Close(),
                    CanExecuteFunc = () => Application.Current.MainWindow != null,
                };
            }
        }

        public ICommand ExitApplicationCommand
        {
            get
            {
                return new DelegateCommand 
                { 
                    CommandAction = () => Application.Current.Shutdown()
                };
            }
        }
    }

    public class DelegateCommand : ICommand
    {
        public Action CommandAction { get; set; }
        public Func<bool> CanExecuteFunc { get; set; }

        public void Execute(object parameter)
        {
            CommandAction();
        }

        public bool CanExecute(object parameter)
        {
            return CanExecuteFunc == null || CanExecuteFunc();
        }

        public event EventHandler CanExecuteChanged
        {
            add 
            { 
                CommandManager.RequerySuggested += value; 
            }
            remove 
            { 
                CommandManager.RequerySuggested -= value; 
            }
        }
    }

}